fix(UI): Fix some bugs when joining an existing cast session (#8452)

Sometimes getAudioTracks, getTextTracks and getVariantTracks returns
null when joining to existing session

Author: avelad

ui/audio_language_selection.js

@@ -63,7 +63,7 @@ shaka.ui.AudioLanguageSelection = class extends shaka.ui.SettingsMenu {
 
   /** @private */
   onAudioTracksChanged_() {
-    const audioTracks = this.player.getAudioTracks();
+    const audioTracks = this.player.getAudioTracks() || [];
 
     shaka.ui.LanguageUtils.updateAudioTracks(audioTracks, this.menu,
         (track) => this.onAudioTrackSelected_(track),

ui/resolution_selection.js

@@ -112,7 +112,7 @@ shaka.ui.ResolutionSelection = class extends shaka.ui.SettingsMenu {
 
   /** @private */
   updateResolutionLabels_() {
-    const tracks = this.player.getVariantTracks();
+    const tracks = this.player.getVariantTracks() || [];
     const track = tracks.find((track) => track.active);
     if (!track) {
       if (this.overflowQualityMark) {
@@ -184,7 +184,7 @@ shaka.ui.ResolutionSelection = class extends shaka.ui.SettingsMenu {
     // When played with src=, the variant tracks available from
     // player.getVariantTracks() represent languages, not resolutions.
     if (this.player.getLoadMode() != shaka.Player.LoadMode.SRC_EQUALS) {
-      tracks = this.player.getVariantTracks();
+      tracks = this.player.getVariantTracks() || [];
     }
 
     // If there is a selected variant track, then we filter out any tracks in

ui/text_selection.js

@@ -128,7 +128,7 @@ shaka.ui.TextSelection = class extends shaka.ui.SettingsMenu {
 
   /** @private */
   updateTextLanguages_() {
-    const tracks = this.player.getTextTracks();
+    const tracks = this.player.getTextTracks() || [];
 
     shaka.ui.LanguageUtils.updateTextTracks(tracks, this.menu,
         (track) => this.onTextTrackSelected_(track),
@@ -206,7 +206,8 @@ shaka.ui.TextSelection = class extends shaka.ui.SettingsMenu {
 
   /** @private */
   onTracksChanged_() {
-    const hasText = this.player.getTextTracks().length > 0;
+    const tracks = this.player.getTextTracks() || [];
+    const hasText = tracks.length > 0;
     shaka.ui.Utils.setDisplay(this.button, hasText);
     this.updateTextLanguages_();
   }